ASK FRED: My Basement Feels Damp. Is There Anything I Can Do Outside to Help with This?
This is a common question that we field in the Washington DC Metro area. The damp “feeling” is caused by cool humid conditions that naturally occur in basements. Typically, there is not as much air flow in the basement. Also, if the house has a central HVAC system, the main return duct is on the main level. There may not be a return duct in the basement at all to help circulate the air.
Regarding the exterior of the house, we look for things like positive slope in the ground and landscape. Water from rain, snow, and runoff, should never slope toward the house. Creating positive slope will let rain, snow, and runoff water naturally run away from the house. In cases where a negative slope exists, over time, the house foundation can leach water into the wall cavity. This water will cause a higher humidity in the basement. In some cases, simply adding clean fill dirt against the foundation can create the desired positive slope.
We will also look at downspouts and gutters. The farther away from the house the downspouts can be run, the better off the foundation will be. Splash blocks and downspout extensions are simple ways to let the water from the roof be carried away from the house foundation. Ensuring that the gutters and downspouts are clear of debris will also help.
Another item to look at is the mulch beds and flower gardens up against the house. Landscape borders like stone walls, brick walls, and edging, can create a scenario that actually keeps water dammed up against the foundation. These types of retaining walls need to have weep holes to let surface water out. Again, positive slope away from the foundation is critical. If your basement “feels” only a little damp, running a dehumidifier could help the space feel more comfortable. If there is a humidifier/dehumidifier with the central HVAC, turning it on and setting it will help as well.